1. Field of the Invention
The present invention relates to a printer having a thermal activating device of a heat sensitive adhesive sheet, for example, used as an adhesive label, in which a heat sensitive adhesive layer for developing adhesion by heating although exhibiting no adhesion at usual is formed on one surface of a sheet-shaped substrate, and more particularly to a forwarding and cutting method of the sheet.
2. Description of the Related Art
In these days, there prevails a stick-on label for use in displaying bar code, price list, and the like, which is made by forming a pressure sensitive adhesive layer on the back side of a recording surface (printing surface) thereof and temporarily attaching a separator on the above layer, hence to be held. In this type of stick-on label, however, the separator has to be peeled off from the pressure sensitive adhesive layer when using it as the label, which never avoids a disadvantage of producing wastes.
Accordingly, as a method of requiring no separator, there has been developed a heat sensitive adhesive label having a heat sensitive adhesive layer on the back surface of a sheet-shaped substrate, the layer exhibiting adhesion by the heating although exhibiting no adhesion at usual, and a thermal activating device for exhibiting the adhesion by heating the heat sensitive adhesive layer on the back surface of the above label.
For example, various heating methods of using a heating roller, a hot air heater, infrared ray emission, an electric heater, a dielectric coil, and the like as heating means are adopted to the thermal activating device. Further, for example, in JP-A-1999-79152, there is disclosed a technique of heating a heat sensitive adhesive layer while making a head contact with a heat sensitive adhesive label, the head having a plurality of resistive elements (heater elements) provided on a ceramic substrate as a heat source, like a thermal head used as a printing head of a thermal printer.
A general structure of the conventional printer for a heat sensitive adhesive sheet will be described with reference to a thermal printer P2 of FIG. 15.
The thermal printer P2 of FIG. 15 comprises a roll case unit 20 for holding a tape-shaped heat sensitive adhesive label 60 reeled like a roll, a printing unit 30 for printing on the heat sensitive adhesive label 60, a cutter unit 40 for cutting the heat sensitive adhesive sheet 60 into a label of a predetermined length, and a thermal activating unit 50 for thermal-activating the heat sensitive adhesive layer of the heat sensitive adhesive label 60 as the thermal activating device.
The heat sensitive adhesive label 60 has constitution that an insulating layer and a heat sensitive coloring layer (printable layer) are formed on the top surface of the sheet substrate, for example, and that a heat sensitive adhesive layer with heat sensitive adhesive applied and dried is formed on the back surface thereof.
The printing unit 30 comprises a printing thermal head 32 including a plurality of heater elements 31 formed by a plurality of comparatively small resistive elements which are aligned in the width direction in a way capable of dot printing, a printing platen roller 33 pushed toward the printing thermal head 32 (heater elements 31), and the like. In FIG. 15, the printing platen roller 33 is rotated clockwise and the heat sensitive adhesive label 60 is forwarded to the right side.
The cutter unit 40 is in order to cut the heat sensitive adhesive label 60 having been printed by the printing unit 30, to a proper length, and it comprises a movable blade 41 operated by a driving source (not illustrated) such as an electric motor, a fixed blade 42 fixed on a side opposite to the movable blade, and the like.
The thermal activating unit 50 comprises a thermal head 52 for thermal activation as heating means having a heater element 51, a platen roller 53 for thermal activation as forwarding means for forwarding the heat sensitive adhesive label 60, drawing rollers 54 for drawing the heat sensitive adhesive label 60 supplied from the side of the printing unit 30 into the space between the thermal head 52 for thermal activation (heater element 51) and the platen roller 53 for thermal activation, and the like. In FIG. 13, the platen roller 53 for thermal activation is rotated in the direction opposite to the printing platen roller 33 (counterclockwise in the drawing), so as to forward the heat sensitive adhesive label 60 in a predetermined direction (right side).
When the heat sensitive adhesive label loosens at a forwarding time, the label becomes wrinkled, or fails in proceeding so often, and therefore, the forwarding speed (printing speed) of the printing platen roller 33 is generally fixed at the same speed as the forwarding speed (activation speed) of the platen roller 53 for thermal activation.
According to thus-constituted thermal printer P2, after the adhesion of the heat sensitive adhesive label 60 is developed, the display label, the price label or advertisement label as it is, can be attached to a cardboard, a food wrap, a glass bottle, a plastic case, and the like. Therefore, a separator for use in the conventional general stick-on label becomes unnecessary and it is effective in reducing the cost. From a view point of the resource saving and the environmental concerns, it is preferable because any separator that will become wastes after use is not required.
In the printer P2 as shown in FIG. 15, however, when the cutter unit 40 performs the cutting operation, it is necessary to stop the forwarding of the heat sensitive adhesive label 60 for the time taken for the vertical movement of the movable blade 41 (for example, 0.4 sec). Namely, the cutter unit 40 performs the cutting operation in a state of stopping the rotation of the printing platen roller 33, the drawing rollers 54, and the platen roller 53 for thermal activation.
Therefore, when the length of a label is longer than the distance from the cut position of the cutter unit 40 to the heater element 51 of the thermal head 52 for thermal activation, the forwarding is stopped in a state of pinching the heat sensitive adhesive label 60 between the thermal head 52 for thermal activation and the platen roller 53 for thermal activation.
As a result, the heat sensitive adhesive layer having the adhesion may be attached to the thermal head 52 for thermal activation (heater element 51) and the label cannot be forwarded smoothly even if the forwarding resumes, thereby causing a disadvantage such as a so-called paper jam or a failure in forwarding. Further, there is a problem of transmitting the heat from the heater element 51 even to the printable layer (heat sensitive coloring layer) of the heat sensitive adhesive label from which the color may run.
In this case, if the label is discharged, since the appearance of the label is ugly, it cannot be used as the stick-on label. Further, if it is fixedly attached, there may be a case of stopping the processing of the printer for the maintenance. Thus, the printer P2 of FIG. 15 is defective in improving the manufacturing efficiency of the stick-on label.